1. Field of the Technology
The technology relates to composite materials, and methods of making these, that include a filler or dopant material, and more especially relates to composite materials that include therein a dispersion of pre-formed, 3D assemblies of nanoparticles.
2. Description of the Related Art
Generally, composite materials include two main components: a polymer and at least one filler material that is either embedded within a matrix of the polymer or that is at least coated with the polymer. The polymer is often an organic polymer, commonly referred to as a “plastic.” The filler material may be selected to produce a composite material with desired physical properties. The filler may have any of a variety of shapes and sizes depending upon the desired nature of the composite. In addition, composite materials may include other components that impart desired properties, such as color, resistance to ultraviolet radiation, or another desirable trait.
Gels are one of a variety of composite materials and gels may include nanoparticle fillers, or “dopants,” as they are called in the aerogel arts. Nanoparticle fillers or dopants may be of any shape, but the major dimension is generally in the size range from about 1 to about 100 nm. From a materials perspective, nanotechnology furnishes composite materials with useful macroscopic properties by manipulating matter in the about 1 to about 100 nm size range. Aerogels are open-cell foams, often derived from drying of wet gels by processes such as supercritical fluid drying processes. Quasi-stable, ultra-low density, three-dimensional assemblies of nanoparticles are referred to as aerogels. The large internal void space of an aerogel is responsible for its low dielectric constant, low thermal conductivity and high acoustic impedance. At the same time, aerogels are generally fragile and impractical for physical high load applications.
In the case of nanoparticle fillers, uniform dispersion throughout the composite material is a desirable goal to provide the composite material with consistent physical properties. Uniform dispersion of nanoparticles presents challenges in practice. These challenges arise from a variety of factors, including, for example, agitation and mixing processes, but also from the differences in physical properties between the nanoparticles and the polymer material, such as density, and properties of the nanoparticles that lead to particle agglomeration.
In general, two issues that often interfere with achieving optimal composite materials performance relate to the non-uniform dispersion (“agglomeration”) of nanoparticles in the polymer and lack of adequate compatibility between the nanoparticles and the polymer. Agglomeration may be so severe as to effectively cancel the advantage of using nano-sized particles because the agglomerates formed may be beyond the nano size range. Lack of materials compatibility, on the other hand, may introduce a discontinuity at the polymer/filler interface where composite failure may initiate when it is deployed in ordinary use.
To date, efforts to address nanoparticle agglomeration generally focused on the use of surfactants that maintain nanoparticle dispersion in the matrix during composite production. Overall, the criterion for success is whether there is any enhancement of the physical properties of the resultant composite beyond what would be obtained by simply mixing nanoparticles into the matrix through agitation, or other mechanical means.